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%load_ext autoreload
%autoreload 2
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import os
import cv2
from perspective_transform import *
from lane_find import *
from color_filtering import *
from calib_camera import *
import glob
import pickle
import matplotlib.pyplot as plt
import numpy as np
from functools import partial
Step by Step Detection of lane lines¶
1. Camera Calibration¶
Calibrate the camera using the images in camera_cal directory
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nx = 9
ny = 6
images = glob.glob("camera_cal/calibration*.jpg")
pickle_file = "camera_cal/dist_pickle.p"
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# Find object and image points and use these to calibrate the camera
objpoints, imgpoints = find_obj_and_img_points(images, nx, ny)
mtx, dist = calibrate_camera(objpoints, imgpoints, (1280, 720))
# save required variables in a pickle file
dict_pickle = dict(objpoints=objpoints, imgpoints=imgpoints, mtx=mtx, dist=dist)
pickle.dump(dict_pickle, open(pickle_file, "wb"))
2. Undistort and transform perspective¶
Let's use one image as an example and transform that into a bird-eye view after undistorting it
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def plot_image(img, cv2_colormap=None, cmap=None, figsize=(24,9)):
if cv2_colormap is not None:
img = cv2.cvtColor(img, cv2_colormap)
plt.figure(figsize=figsize)
plt.imshow(img, cmap)
plot_color_image = partial(plot_image, cv2_colormap=cv2.COLOR_BGR2RGB)
plot_gray_image = partial(plot_image, cv2_colormap=cv2.COLOR_BGR2GRAY)
plot_bw_image = partial(plot_image, cmap="gray")
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fnames = os.listdir("test_images")
idx = 5
fname = fnames[idx]
print(fname)
img = cv2.imread(os.path.join("test_images", fname))
plot_color_image(img)
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# first load mtx and dist
pickle_file = "camera_cal/dist_pickle.p"
dict_pickle = pickle.load(open(pickle_file, "rb"))
mtx, dist = dict_pickle["mtx"], dict_pickle["dist"]
I experimented with various values for the source and destination polygons and have found these settings to provide reasonable results
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src = np.float32(
[[ 585, 460],
[ 203, 720],
[1126, 720],
[ 695, 460]])
dst = np.float32(
[[350, 0.],
[350, 720.],
[950, 720.],
[950, 0.]])
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warped_img, M = streetview2birdview(img, mtx, dist, src, dst, img_size=(img.shape[1], img.shape[0]))
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plot_color_image(warped_img) # seems plausible
plt.savefig("examples/warped.jpg", bbox_inches="tight")
Step 3: Color Thresholding¶
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# Define various color thresholded binary images using different filters
grad_binary = abs_sobel_thresh(warped_img, orient='x', thresh=(20, 100), sobel_kernel=3)
mag_binary = mag_thresh(warped_img, thresh=(30, 100), sobel_kernel=3)
dir_binary = dir_thresh(warped_img, thresh=(0.7, 1.3), sobel_kernel=15)
s_binary = hls_thresh(warped_img, hls_channel="S", thresh=(90, 255))
l_binary = hls_thresh(warped_img, hls_channel="L", thresh=(30, 100))
r_binary = rgb_thresh(warped_img, rgb_channel="R", thresh=(200, 255))
assert grad_binary.shape == mag_binary.shape == dir_binary.shape == s_binary.shape == warped_img.shape[:2]
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f, axes = plt.subplots(2, 3, figsize=(24, 9))
# f.tight_layout()
axes[0][0].imshow(grad_binary, cmap="gray")
axes[0][0].set_title('Grad. Abs', fontsize=50)
axes[0][1].imshow(mag_binary, cmap='gray')
axes[0][1].set_title('Grad Magn.', fontsize=50)
axes[0][2].imshow(dir_binary, cmap='gray')
axes[0][2].set_title('Grad Dir.', fontsize=50)
axes[1][0].imshow(s_binary, cmap='gray')
axes[1][0].set_title('S Channel', fontsize=50)
axes[1][1].imshow(l_binary, cmap='gray')
axes[1][1].set_title('L Channel', fontsize=50)
axes[1][2].imshow(r_binary, cmap='gray')
axes[1][2].set_title('R Channel', fontsize=50)
plt.subplots_adjust(left=0., right=1, top=1.4, bottom=0.)
f.savefig("examples/color_thresh.jpg", bbox_inches='tight')
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# Combine thresholds, e.g. using the S and R channel
combined_binary = np.zeros_like(dir_binary)
# combined_binary[((hls_binary == 1) & (l_binary==0)) | (r_binary==1) | ((grad_binary == 1) | ((mag_binary == 1) & (dir_binary == 0)))] = 1
combined_binary[((s_binary == 1) | (r_binary==1))] = 1
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f, (ax1, ax2) = plt.subplots(1,2, figsize=(24, 9))
f.tight_layout()
ax1.imshow(cv2.cvtColor(warped_img, cv2.COLOR_BGR2RGB))
ax1.set_title('Original image', fontsize=50)
ax2.imshow(combined_binary, cmap='gray')
ax2.set_title('Combined thresh.', fontsize=50)
plt.subplots_adjust(left=0., right=1, top=0.9, bottom=0.)
f.savefig("examples/combined_thresh.jpg", bbox_inches="tight")
Step 4: Find lane lines¶
From Scratch
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left_fitx, right_fitx, left_fit, right_fit, ploty, out_img, detected_flag = find_lanes_from_scratch(combined_binary, draw_lanes=True)
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plot_image(out_img)
plt.savefig("examples/sliding_windows.jpg", bbox_inches="tight")
# red and blue are the detected pixels of left and right lane, respectively
# yellow is the fitted polynomial of second order to these pixels
# green denotes the sliding windows for finding the lane pixels
From Prior Search
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# Note that when applied on videos, the previous image needs to be passed as input
left_fitx, right_fitx, _, _, ploty, out_img, detected_flag = find_lanes_from_prior(combined_binary, left_fit, right_fit)
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plot_image(out_img)
plt.savefig("examples/lane_margin.jpg", bbox_inches="tight")
# green denotes the margin around which the lanes are searched from the previously detected lane
5. Calculate lane curvature and offset from road center¶
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left_curverad, right_curverad = measure_curvature(ploty, left_fitx, right_fitx)
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print(f"left curve radius: {left_curverad}m, right curve radius: {right_curverad}m")
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offset = measure_offset(left_fitx, right_fitx, midpoint=out_img.shape[1]//2)
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print(f"Offset is {offset}m")
6. Warp back detected lanes to original image¶
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img_with_lane = birdview2streetview(out_img, img, combined_binary, dst, src, left_fitx, right_fitx, ploty)
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plot_image(img_with_lane)
7. Project curvatures and offset values onto image¶
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img_with_lane = show_crv_and_offset(img_with_lane, left_curverad, right_curverad, offset)
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plot_image(img_with_lane)
plt.savefig("examples/warped_back.jpg", bbox_inches="tight")
Pipeline¶
Let's go through the entire lane detection pipeline on all the images in test_images folder and save the result to output_images
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# Run the previous cells from above to obtain mtx, dist, src and dst
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# Let's define some helper functions/wrappers
def warp_to_orig(out_img, orig_img, combined_binary, dst, src, left_fitx, right_fitx, ploty, left_crv, right_crv, offset):
img_with_lane = birdview2streetview(out_img, orig_img, combined_binary, dst, src, left_fitx, right_fitx, ploty)
img_with_lane = show_crv_and_offset(img_with_lane, left_crv, right_crv, offset)
return img_with_lane
def hls_rgb_thresh(img, hls_channel, rgb_channel, hls_threshold, rgb_threshold):
# For the sake of demonstration, let's only use the thresholding from HLS and RGB space
s_binary = hls_thresh(img, hls_channel=hls_channel, thresh=hls_threshold)
r_binary = rgb_thresh(img, rgb_channel=rgb_channel, thresh=rgb_threshold)
combined_binary = np.zeros_like(s_binary)
combined_binary[((s_binary == 1) | (r_binary==1))] = 1
return combined_binary
def calc_lane_crv_and_offset(left_fitx, right_fitx, ploty, midpoint):
left_curverad, right_curverad = measure_curvature(ploty, left_fitx, right_fitx)
offset = measure_offset(left_fitx, right_fitx, midpoint)
return left_curverad, right_curverad, offset
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# First we define a wrapper function for the entire pipeline
# Note that the camera does not need to be calibrated again
def lane_detection_pipeline(img, warp_func, color_thresh_func, find_lanes_func, calc_lane_params_func, warp_back_func):
# Transform to bird-eye perspective
warped_img, M = warp_func(img)
# Color Threshold
combined_binary = color_thresh_func(warped_img)
# Detect lane lines (for the sake of this exercise, let's do it from scratch)
left_fitx, right_fitx, left_fit, right_fit, ploty, out_img, detected_flag = find_lanes_func(combined_binary)
# Calculate curvature and offset
left_curverad, right_curverad, offset = calc_lane_params_func(left_fitx, right_fitx, ploty)
# Warp back to original image and project onto original image
img_with_lane = warp_back_func(out_img=out_img, orig_img=img, combined_binary=combined_binary, left_fitx=left_fitx,
right_fitx=right_fitx, ploty=ploty, left_crv=left_curverad, right_crv=right_curverad, offset=offset)
# Return all intermediate steps for visualization
return warped_img, combined_binary, out_img, img_with_lane
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warp = partial(streetview2birdview, mtx=mtx, dist=dist, src=src, dst=dst, img_size=(1280, 720))
color_thresh = partial(hls_rgb_thresh, hls_channel="S", rgb_channel="R", hls_threshold=(90, 255), rgb_threshold=(200, 255))
calc_lane_params = partial(calc_lane_crv_and_offset, midpoint=640)
warp_back = partial(warp_to_orig, dst=dst, src=src)
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def plot_pipeline(fname, warped_img, combined_binary, out_img, img_with_lane, savefig=True):
img = cv2.imread(os.path.join("test_images", fname))
f, (ax0, ax1, ax2, ax3, ax4) = plt.subplots(1,5, figsize=(24, 9))
f.tight_layout()
ax0.imshow(cv2.cvtColor(img, cv2.COLOR_BGR2RGB))
ax0.set_title(f'{fname}', fontsize=20)
ax1.imshow(cv2.cvtColor(warped_img, cv2.COLOR_BGR2RGB))
ax1.set_title('Warped', fontsize=20)
ax2.imshow(combined_binary, cmap='gray')
ax2.set_title('Combined thresh.', fontsize=20)
ax3.imshow(out_img, cmap='gray')
ax3.set_title('Lane pixels', fontsize=20)
ax4.imshow(img_with_lane)
ax4.set_title('Detected lanes', fontsize=20)
plt.subplots_adjust(left=0., right=1, top=0.9, bottom=0.)
if savefig:
out_file = os.path.join("output_images", f"{fname[:-4]}_warped.jpg")
cv2.imwrite(out_file, cv2.cvtColor(warped_img, cv2.COLOR_BGR2RGB))
out_file = os.path.join("output_images", f"{fname[:-4]}_colorthresh.jpg")
cv2.imwrite(out_file, combined_binary*255)
out_file = os.path.join("output_images", f"{fname[:-4]}_lanesearch.jpg")
cv2.imwrite(out_file, cv2.cvtColor(out_img, cv2.COLOR_BGR2RGB))
out_file = os.path.join("output_images", f"{fname[:-4]}_withlanes.jpg")
cv2.imwrite(out_file, cv2.cvtColor(img_with_lane, cv2.COLOR_RGB2BGR))
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warped_img, combined_binary, out_img, img_with_lane = lane_detection_pipeline(img, warp_func=warp,
color_thresh_func=color_thresh,
find_lanes_func=find_lanes_from_scratch,
calc_lane_params_func=calc_lane_params,
warp_back_func=warp_back)
In [56]:
for fname in fnames:
img = cv2.imread(os.path.join("test_images", fname))
warped_img, combined_binary, out_img, img_with_lane = lane_detection_pipeline(img, warp_func=warp,
color_thresh_func=color_thresh,
find_lanes_func=find_lanes_from_scratch,
calc_lane_params_func=calc_lane_params,
warp_back_func=warp_back)
plot_pipeline(fname, warped_img, combined_binary, out_img, img_with_lane)
We can see that the R channel filter in RGB space produces very clear images of both lines under optimal lighting conditions. However when there are shadows or reflections the R-filtered image is quite "noisy". Therefore it seems to be that this type of filter is not robust to changing environments. In the following video pipeline, we will use a different type of color thresholding
Test on video¶
First let's define a class which stores attributes across frames. I will use the example class proposed in the lecture materials with some slight modifications (e.g. I won't be using all of the attributes)
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#import imageio
#imageio.plugins.ffmpeg.download()
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# Import everything needed to edit/save/watch video clips
from moviepy.editor import VideoFileClip
from IPython.display import HTML
In [35]:
# Define a class to receive the characteristics of each line detection
class Line():
def __init__(self):
# was the line detected in the last iteration?
self.detected = False
# x values of the last n fits of the line
self.recent_xfitted = []
#polynomial coefficients for the most recent fit
# self.current_fit = [np.array([False])]
self.current_fit = None
#radius of curvature of the line in some units
self.radius_of_curvature = None
#distance in meters of vehicle center from the line
self.line_base_pos = None
# incremental counter for frames where a lane line has not been found
self.not_found_counter = 0
# dummy flag which indicates that for the first frame of the video, the lane line has to be detected from scratch
self.initial_scratch_search = True
# threshold for the number of continuous frames with no lane lines detected (if this threshold is reached, a search from scratch will be triggered)
self.continuous_frames_with_no_lanes = 5
# an incremental counter for the number of frames, resets to 0 if the buffer is reached
self.frame_counter = 0
# length of continuous frames which are stored in a buffer; determines length of self.recent_xfitted
self.frame_buffer = 12
Idea¶
The idea for detecting lanes is to find them from prior frames as much as possible. However that function does not necessarily need to detect a lane, as opposed to finding lanes from scratch function which always has to find a lane.
We introduce an additional function output (also see above and the lane_find.py module) called the detected_flag which indicates if a lane has been found. This flag will be saved as a class attribute for each frame.
For the following video pipeline, I have tested the switch from finding lanes from prior frames to finding lanes from scratch by setting a very small search margin. If the margin is too small (e.g. 10 - 20 pixels) then we can enforce a search from scratch.
Also I have introduced additional class attributes for smoothing lanes. I'm saving the x-values of the fitted polynomials for the last 12 frames. Then I'm taking the median (as opposed to the mean in order to counter the effect of possible outliers) of those polynoms as the lane polynom for the current frame. This makes the detected lanes less noisy and appear more smooth across frames.
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# this function stores a list which contains exactly list_len items;
# if the list contains less items it appends new items to the end of the list, if it contains five items it choses the item of index "index" to be replaced by the newest item
# this function is used in the video processing pipeline
def append_or_replace(l_list, index, item, list_len=5):
if len(l_list)<list_len:
l_list.append(item)
else:
l_list[index] = item
assert len(l_list)<=list_len
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def process_video(image):
# transform image to birds-eye perspective
warped_img, M = streetview2birdview(image, mtx, dist, src, dst, img_size=(image.shape[1], image.shape[0]))
# calculate color thresholds; here we use sobel filter in x direction, magnitude threshold, direction threshold and S channel threshold
grad_binary = abs_sobel_thresh(warped_img, orient='x', thresh=(20, 100), sobel_kernel=3)
mag_binary = mag_thresh(warped_img, thresh=(30, 100), sobel_kernel=3)
dir_binary = dir_thresh(warped_img, thresh=(0.7, 1.3), sobel_kernel=15)
s_binary = hls_thresh(warped_img, hls_channel="S", thresh=(90, 255))
combined_binary = np.zeros_like(dir_binary)
combined_binary[(grad_binary == 1) | (s_binary == 1) | ( ((mag_binary == 1) & (dir_binary == 0)))] = 1
# Search for lane lines: Enforce search from scratch on frame 0
if leftlane.initial_scratch_search or rightlane.initial_scratch_search:
left_fitx, right_fitx, left_fit, right_fit, ploty, out_img, detected_flag = find_lanes_from_scratch(combined_binary)
leftlane.detected, rightlane.detected = True, True
leftlane.current_fit, rightlane.current_fit = left_fit, right_fit
leftlane.initial_scratch_search, rightlane.initial_scratch_search = False, False
# if no lane detected, increase the counter of frames with no lanes found; if the counter exceeds threshold search again from scratch
if not leftlane.detected or not rightlane.detected:
leftlane.not_found_counter += 1
rightlane.not_found_counter += 1
# if no lane lines found, simply return the image with curvature and offset parameters printed (these will be obtained from the last time the radius and offset were calculated)
if leftlane.not_found_counter < leftlane.continuous_frames_with_no_lanes:
result = show_crv_and_offset(image, leftlane.radius_of_curvature, rightlane.radius_of_curvature, leftlane.line_base_pos)
return result
# search from scratch if threshold for no lanes found is exceeded
else:
left_fitx, right_fitx, left_fit, right_fit, ploty, out_img, detected_flag = find_lanes_from_scratch(combined_binary)
leftlane.detected, rightlane.detected = True, True
leftlane.current_fit, rightlane.current_fit = left_fit, right_fit
leftlane.not_found_counter, rightlane.not_found_counter = 0, 0 # reset counter
else: # if lanes detected previously, simply search from previous frame around margin
left_fitx, right_fitx, leftlane.current_fit, rightlane.current_fit, ploty, out_img, detected_flag = find_lanes_from_prior(combined_binary, leftlane.current_fit, rightlane.current_fit, margin=100)
leftlane.detected = detected_flag
rightlane.detected = detected_flag
leftlane.not_found_counter, rightlane.not_found_counter = 0, 0 # reset counter of frames with no lane lines found
# store fitted pixels of lanes in list using a FIFO (first in, first out) rule; oldest pixel values will be replaced
append_or_replace(leftlane.recent_xfitted, leftlane.frame_counter%leftlane.frame_buffer, left_fitx, list_len=leftlane.frame_buffer)
append_or_replace(rightlane.recent_xfitted, rightlane.frame_counter%rightlane.frame_buffer, right_fitx, list_len=rightlane.frame_buffer)
# use median of all pixel values in list as actual fit
try: # to avoid a bad start (might happen when margin is set too small)
left_fitx = np.median(np.array([x for x in leftlane.recent_xfitted if x is not None]), axis=0) # using median because more robust against outliers
right_fitx = np.median(np.array([x for x in rightlane.recent_xfitted if x is not None]), axis=0)
except:
pass
# calculate road parameters, save in class attributes and display on image with warped back lane lines
try:
left_curverad, right_curverad = measure_curvature(ploty, left_fitx, right_fitx)
offset = measure_offset(left_fitx, right_fitx, midpoint=out_img.shape[1]//2)
leftlane.radius_of_curvature, rightlane.radius_of_curvature = left_curverad, right_curverad
leftlane.line_base_pos, rightlane.line_base_pos = offset, offset
img_with_lane = birdview2streetview(out_img, image, combined_binary, dst, src, left_fitx, right_fitx, ploty)
result = show_crv_and_offset(img_with_lane, leftlane.radius_of_curvature, rightlane.radius_of_curvature, leftlane.line_base_pos)
except: # if not possible, simply use image without lane lines
result = show_crv_and_offset(image, leftlane.radius_of_curvature, rightlane.radius_of_curvature, leftlane.line_base_pos)
# increase counter for frames
leftlane.frame_counter+=1
rightlane.frame_counter+=1
# if frame counter reaches buffer threshold, reset
if leftlane.frame_counter == leftlane.frame_buffer or rightlane.frame_counter == rightlane.frame_buffer:
leftlane.frame_counter, rightlane.frame_counter = 0, 0
return cv2.cvtColor(result, cv2.COLOR_BGR2RGB)
Let's run the pipeline on the project video
In [46]:
leftlane = Line()
rightlane = Line()
input_video = './project_video.mp4'
output_video = './project_video_result.mp4'
clip1 = VideoFileClip(input_video)
white_clip = clip1.fl_image(process_video)
%time white_clip.write_videofile(output_video, audio=False, progress_bar=False)
In [47]:
HTML("""
<video width="640" height="360" controls>
<source src="{0}">
</video>
""".format(output_video))
Out[47]:
Let's try it on the challenge video
In [48]:
leftlane = Line()
rightlane = Line()
input_video = './challenge_video.mp4'
output_video = './challenge_video_result.mp4'
clip1 = VideoFileClip(input_video)
white_clip = clip1.fl_image(process_video)
%time white_clip.write_videofile(output_video, audio=False, progress_bar=False)
In [49]:
HTML("""
<video width="640" height="360" controls>
<source src="{0}">
</video>
""".format(output_video))
Out[49]:
Smoothing across previous frames actually helps in this case; the lane lines less noisy and jump around less from frame to frame
Finally, on the most difficult challenge video
In [50]:
leftlane = Line()
rightlane = Line()
input_video = './harder_challenge_video.mp4'
output_video = './harder_challenge_video_result.mp4'
clip1 = VideoFileClip(input_video)
white_clip = clip1.fl_image(process_video)
%time white_clip.write_videofile(output_video, audio=False, progress_bar=False)
In [51]:
HTML("""
<video width="640" height="360" controls>
<source src="{0}">
</video>
""".format(output_video))
Out[51]:
One can see that the lane detection algorithm does not work well on the last video (possibly due to extreme changes in lighting, lots of shadows, quick curve changes)
Ideas for improving the pipeline¶
separate the search of the left and right lane lines: currently both are done in the same function. However it could be the case that only one of the lane lines is found. In that case there is no need to trigger a re-search from scratch for both lane lines, but only for the one which has not been found.
deal with intersecting lane lines: sometimes when the lines are detected incorrectly (left lane curves to the right, right lane curves to the left), the left lane and right lane will intersect. In this case one could add a sanity check for detecting cases where the minimum x-pixel of the right lane is smaller than the maximum x-pixel of the left lane (meaning intersection). When that happens one could trigger a search from scratch or use a smaller src/dst polygon for the warping
calculate lane width: an additional check would be to calculate lane width (right lane x-pixel minus left lane x-pixel); if it's too wide (e.g. right lane detected outside the actual lane) one could start a search from scratch
- alternative approach to smoothing lanes across frames: in my current approach I am returning the left_fitx and right_fitx values from the already fit polynomes and average across those values; an alternative approach would be to return the leftx and rightx pixel values, average across those and then fit a polynom on the averaged pixels
- diverging curvatures: if the curvatures of left and right lane lines diverge too much (let's say a factor of 10), one can mirror the polynom of either the left or right lane to the other side
- fit more complex polynomial: under extreme curve situations (tight left curve followed directly by tight right curve), a polynomial of second degree does not properly represent the curvature anymore, in that case a more complex polynom might be more fitting
- better parameter tuning: there are many parameters which can be more carefully tuned (such as the size of the warping polynoms src and dst, the thresholds for the filters etc.). Or one could use a set of multiple parameters for multiple situations or even dynamic parameters.